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    <title>cl_khr_subgroups</title>
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        <a xmlns="http://www.w3.org/1999/xhtml" id="cl_khr_subgroups"></a>
        <h1>cl_khr_subgroups</h1>
        <p>
            Extension adds support for implementation-controlled subgroups.
        </p>
      </div>
      <div class="refsect2">
        <a id="synopsis"></a>
        <h3>
        </h3>
        <div class="informaltable">
          <table border="0">
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              <col align="left" class="col1" />
            </colgroup>
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              <tr>
                <td align="left">
#pragma OPENCL EXTENSION cl_khr_subgroups : enable
                        </td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
            Subgroups behave similarly to workgroups with their own 
            sets of builtins and synchronization primitives. Subgroups 
            within a workgroup are independent, make forward progress 
            with respect to each other and may map to optimized 
            hardware structures where that makes sense.
        </p>
        <p>
            If this extension is supported by an implementation, 
            the string <code class="code">cl_khr_subgroups</code> will be 
            present in the <code class="constant">CL_DEVICE_EXTENSIONS</code> 
            string described in table 4.3
            (see <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>).
        </p>
        <p>
            Within a work-group work-items may be divided 
            into sub-groups in an implementation-defined 
            fashion. The mapping of work-items to sub-groups 
            is implementation-defined and may be 
            queried at runtime. While sub-groups may be 
            used in multi-dimensional work-groups, 
            each subgroup is 1-dimensional and any given 
            work-item may query which sub-group it is a member of.
        </p>
        <p>
            Work items are mapped into subgroups through 
            a combination of compile-time decisions and the 
            parameters of the dispatch. The mapping to subgroups 
            is invariant for the duration of a kernel’s 
            execution, across dispatches of a given kernel 
            with the same launch parameters, and from one 
            work-group to another within the dispatch (excluding 
            the trailing edge work-groups in the
            presence of non-uniform work-group sizes). In 
            addition, all sub-groups within a work-group will 
            be the same size, apart from the sub-group with 
            the maximum index which may be smaller if the 
            size of the work-group is not evenly divisible 
            by the size of the sub-groups
        </p>
        <p>
            Sub-groups execute concurrently within a given work-group 
            and make independent forward progress with respect to each 
            other even in the absence of work-group barrier operations. 
            Subgroups are able to internally synchronize using barrier 
            operations without synchronizing with each other.
        </p>
        <p>
            In the degenerate case, with the extension enabled, a single 
            sub-group must be supported for each work-group. In this 
            situation all sub-group scope functions alias their work-group 
            level equivalents.
        </p>
        <p>
            This extension enables the following functions:
        </p>
        <div class="informaltable">
          <table border="1">
            <colgroup>
              <col align="left" class="col1" />
              <col align="left" class="col2" />
            </colgroup>
            <tbody>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="clGetKernelSubGroupInfoKHR.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">clGetKernelSubGroupInfoKHR</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns information about the kernel object</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_sub_group_size.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_sub_group_size</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the number of work-items in the subgroup</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_max_sub_group_size.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_max_sub_group_size</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the maximum size of a subgroup within the dispatch</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_num_sub_groups.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_num_sub_groups</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the number of subgroups in the current workgroup</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_enqueued_num_sub_groups.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_enqueued_num_sub_groups</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the number of enqueued subgroups</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_sub_group_id.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_sub_group_id</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the sub-group ID</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_sub_group_local_id.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_sub_group_local_id</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the unique work-item ID within the current subgroup</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_barrier.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_barrier</span>
                    </span>
                  </a>
                </td>
                <td align="left">Sub-group barrier</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_all.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_all</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns non-zero if a predicate evaluates true for all work-items</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_any.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_any</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns non-zero if a predicate evaluates true for any work-items</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_broadcast.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_broadcast</span>
                    </span>
                  </a>
                </td>
                <td align="left">Broadcast a value to all work-items in a sub-group</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_reduce.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_reduce_&lt;op&gt;</span>
                    </span>
                  </a>
                </td>
                <td align="left">Broadcast a value to all work-items in a sub-group</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_scan_exclusive.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_scan_exclusive_&lt;op&gt;</span>
                    </span>
                  </a>
                </td>
                <td align="left">Do an exclusive scan operation</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_scan_inclusive.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_scan_inclusive_&lt;op&gt;</span>
                    </span>
                  </a>
                </td>
                <td align="left">Do an inclusive scan operation</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_reserve_read_pipe.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_reserve_read_pipe</span>
                    </span>
                  </a>
                </td>
                <td align="left">Reserve packet entries for reading from a pipe</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_reserve_write_pipe.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_reserve_write_pipe</span>
                    </span>
                  </a>
                </td>
                <td align="left">Reserve packet entries for writing to a pipe</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_commit_read_pipe.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_commit_read_pipe</span>
                    </span>
                  </a>
                </td>
                <td align="left">Indicates that all reads associated with a reservation are completed</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="sub_group_commit_write_pipe.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">sub_group_commit_write_pipe</span>
                    </span>
                  </a>
                </td>
                <td align="left">Indicates that all writes associated with a reservation are completed</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_kernel_sub_group_count_for_ndrange.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_kernel_sub_group_count_for_ndrange</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the number of subgroups in each workgroup of the dispatch</td>
              </tr>
              <tr>
                <td align="left">
                  <a class="citerefentry" href="get_kernel_max_sub_group_size_for_ndrange.html">
                    <span class="citerefentry">
                      <span class="refentrytitle">get_kernel_max_sub_group_size_for_ndrange</span>
                    </span>
                  </a>
                </td>
                <td align="left">Returns the maximum sub-group size for a block</td>
              </tr>
            </tbody>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />

            <a href="https://www.khronos.org/registry/cl/specs/opencl-2.0-extensions.pdf#page=133" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="EXTENSION.html"><span class="citerefentry"><span class="refentrytitle">EXTENSION</span></span></a>,
            <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>,
            <a class="citerefentry" href="clGetKernelSubGroupInfoKHR.html"><span class="citerefentry"><span class="refentrytitle">clGetKernelSubGroupInfoKHR</span></span></a>,
            <a class="citerefentry" href="workItemFunctions.html"><span class="citerefentry"><span class="refentrytitle">Work Item Functions</span></span></a>,
            <a class="citerefentry" href="syncFunctions.html"><span class="citerefentry"><span class="refentrytitle">Sync Functions</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2013 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
permit persons to whom the Materials are furnished to do so, subject to
the condition that this copyright notice and permission notice shall be included
in all copies or substantial portions of the Materials.
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